1. Field of the Invention
The present invention relates to an inkjet head in which pressure chambers are arranged in a matrix.
2. Description of Related Art
JP-A-2003-237078 discloses an inkjet head in which a large number of pressure chambers are arranged in a matrix. Upper section of FIG. 21 shows a schematic view of an arrangement of nozzles of inkjet head used as a line head. In the inkjet head of upper section of FIG. 21, each of belt-like regions R defined by a large number of straight lines extending in a paper conveyance direction, i.e., a sub scanning direction, includes therein sixteen nozzles 108. The sixteen nozzles 108 differ from one another in coordinate value in a head longitudinal direction, i.e., a main scanning direction, and coordinate value in the paper conveyance direction, i.e., the sub scanning direction. Sixteen points obtained by projecting the sixteen nozzles 108 from the sub scanning direction on an imaginary straight line extending in the main scanning direction, are arranged at regular intervals corresponding to resolution of print. When the nozzles are numbered by (1) to (16) in order from the left of the arrangement of the corresponding projection points, the sixteen nozzles 108 are arranged in the order of (1), (9), (5), (13), (2), (10), (6), (14), (3), (11), (7), (15), (4), (12), (8), and (16) from the lower side. When each belt-like region R is equally divided into four sub regions r1, r2, r3, and r4 by straight lines extending in the sub scanning direction, each sub region includes therein four nozzles 108 arranged on a straight line. Any belt-like region R has the same arrangement of sixteen nozzles 108.
In this inkjet head, when ink is ejected from the nozzles 108 in order at short ejection intervals onto a paper being conveyed, as shown in middle section of FIG. 21, a large number of straight lines can be printed that extend in the sub scanning direction and are arranged at the same regular intervals as the intervals between the above-described projection points. Because each interval between the straight lines is narrow, the region in which the large number of straight lines have been printed can be practically observed as if it is a solid region.
In the inkjet head disclosed in JP-A-2003-237078, as shown in upper section of FIG. 21, a nozzle (1) belonging to a belt-like region R is at a very long distance in the sub scanning direction from a nozzle (16) belonging to the left neighboring belt-like region R. Therefore, if a large number of straight lines as shown in middle section of FIG. 21 are printed with the inkjet head having been attached at a somewhat incorrect angle, as shown in lower section of FIG. 21, the interval between the straight line formed by ink ejected from the nozzle (1) and the straight line formed by ink ejected from the nozzle (16) may be wider than the intervals between the other straight lines. As a result, periodic white stripes 101, called banding, appear on the print. This gives an observer an uncomfortable feeling.
To avoid banding, the inkjet head must be attached to the main body of a printer with very high accuracy. However, a process for attaching the inkjet head with high accuracy may cause complication of the manufacture process of the printer and an increase in cost.